There is a need for some means or method to prevent young children and other unauthorized persons from using electrically operated devices, and particularly power tools, which might cause injury or harm to them and/or damage to the electrical appliance involved.
In the home there are power tools in the basement workshop, power operated garden tools out in the garage, electric knives and mixers in the kitchen, hair dryers and curlers in the bathrooms, all of which are potentially dangerous to young children and even older children who haven't been taught how to use them.
In offices and shops there are certain electrically operated devices that are best left to experienced and trained personnel. In retail appliance stores, only demonstrator models should be operable without a sales person in attendance. And, certain sophisticated electronics devices are tagged with warnings that they should not be plugged in after delivery until they have first been properly serviced and set-up.
Obviously, it is not practical to have built in key locking devices in all such appliances, nor is it practical to expect that any of the commonly known key or combination locks will be used in either storing away such equipment or in preventing their use, as by some lock box on the plug-in end of their electrical cords.
There are plug-in and rotatable closures for use in the electrical wall outlets in rooms where small children play and might stick something into a wall socket, but it is not practical to have these all over the house and many of the items mentioned are portable and can be carried to a socket that is not so protected. Such devices are also overly simple and easily operable by children, once they see how it is done, and would be no discouragement whatsoever in those instances involving inquisitive adults who "just have to try" whatever it is they are curious about and find unattended.
From a consideration of the forgoing, what appears to be needed in some relatively simple device, which can be inexpensively made, and that will fit over the end of the electrical cord, and enclose the plug, or otherwise make it inoperative. Also, that such a device require both some dexterity, to foil the efforts of younger children, and if possible some sort of key device, of a simple nature, to discourage all others that might otherwise be tempted to tamper with the protected tool, appliance or whatever it may be.